Priority is claimed to Great Britain patent application No. 9930000.6 filed on Dec. 21, 1999.
The present invention relates to an ingestible device. In particular the invention relates to such a device in the form of a capsule that is intended to release a controlled quantity of a substance, such as a pharmaceutically active compound, foodstuff, dye, radiolabelled marker, vaccine, physiological marker or diagnostic agent at a chosen location in the gastrointestinal (GI) tract of a mammal. Such a capsule is sometimes referred to as a xe2x80x9cSite-Specific Delivery Capsulexe2x80x9d, or SSDC.
SSDC ""s have numerous uses. One use of particular interest to the pharmaceutical industry involves assessing the absorption rate and/or efficacy of a compound under investigation, at various locations in the GI tract. Pharmaceutical companies can use data obtained from such investigations, e.g. to improve commercially produced products.
Several designs of SSDC are known. One design of capsule intended for use in the GI tract of a mammal is disclosed in xe2x80x9cAutonomous Telemetric Capsule to Explore the Small Bowelxe2x80x9d, Lambert et al, Medical and Biological Engineering and Computing, March 1991. The capsule shown therein exhibits several features usually found in such devices, namely:
a reservoir for a substance to be discharged into the GI tract;
an on-board energy source;
a mechanism, operable under power from the energy source, for initiating discharge of the substance from the reservoir;
a switch, operable remotely from outside the body of the mammal, for initiating the discharge; and
a telemetry device for transmitting data indicative of the status, location
and/or orientation of the capsule.
Also, of course, the dimensions of the capsule are such as to permit its ingestion via the oesophagus; and the external components of the capsule are such as to be biocompatible for the residence time of the capsule within the body.
The capsule disclosed by Lambert et al suffers several disadvantages. Principal amongst these is the complexity of the device. This means that the capsule is expensive to manufacture. Also the complexity means that the capsule is prone to malfunction.
For example, the capsule disclosed by Lambert et al includes a telemetry device that is initially retracted within a smooth outer housing, to permit swallowing of the capsule via the oesophagus. Once the capsule reaches the stomach, gastric juice destroys a gelatin seal retaining the telemetry device within the housing. The telemetry device then extends from the housing and presents a rotatable star wheel that engages the wall of the GI tract. Rotations of the star wheel generate signals that are transmitted externally of the capsule by means of an on-board RF transmitter powered by a battery within the capsule housing.
This arrangement may become unreliable when used in mammals whose GI motility is poor or whose gastric juice composition is abnormal.
There is a risk of malfunction of the rotating part of the telemetry device, and the method of operation of the capsule is generally complex.
The space needed to house the telemetry device within the capsule during swallowing/ingestion is unusable for any other purpose when the telemetry device is extended. Therefore the Lambert et al capsule is not space-efficient. This is a serious drawback when considering the requirement for the capsule to be as small as possible to aid ingestion.
Also the Lambert et al disclosure details the use of a high frequency ( greater than 100 MHz) radio transmitter for remotely triggering the release of the substance from the capsule into the GI tract. The use of such high frequencies is associated with disadvantages, as follows:
When power is transmitted to the capsule whilst it is inside the GI tract the energy must pass through the tissue of the mammal that has swallowed the capsule. The transmission of this power through the body of the mammal may result in possible interactions with the tissue which at some power levels may lead to potential damage to that tissue.
The higher the frequency of energy transmission the higher the coupled power for a given field strength. However, as the frequency is increased the absorption of the energy by the body tissue also increases. The guidelines for the exposure of humans to static and time varying electromagnetic fields and radiation for the UK are given in the National Radiological Protection Board (NRPB) publication xe2x80x9cOccupational Exposure to Electromagnetic fields: Practical Application of NRPB Guidancexe2x80x9d NRPB-R301. This describes two mechanisms of interaction: induced currents and direct heating measured in terms of the SAR (specific energy absorption rate). In general terms the induced current dominates up to 2 MHz above which the SAR effects take over.
An ingestible device for delivering a substance to a chosen location in the GI tract of a mammal includes a receiver of electromagnetic radiation for powering an openable part of the device to an opened position for dispensing of the substance. The receiver includes a coiled wire that couples the energy field, the wire having an air or ferrite core.
In a further embodiment the invention includes an apparatus for generating the electromagnetic radiation, the apparatus including one or more pairs of field coils supported in a housing.
The device optionally includes a latch defined by a heating resistor and a fusible restraint. The device may also include a flexible member that may serve one or both the functions of activating a transmitter circuit to indicate dispensing of the substance; and restraining of a piston used for expelling the substance.
According to a first aspect of the invention, there is provided an ingestible device for delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator from the energy source; and a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range, the receiver including an air core having coiled therearound a wire; characterised in that the coiled wire lies on or is embedded in an outer wall of the device.
This arrangement advantageously permits the use of an oscillating magnetic field as an external energy source for remotely triggering e.g. the release of a compound from the capsule. For reasons discussed below, a magnetic field offers advantages over a field including radio waves.
Preferably the housing defined ingestible device for delivering a substance to a chosen or indentifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, an actuator mechanism, an energy source, a releasable latch and a receiver of electromagnetic radiation is cylindrical. Other, non-circular section housings e.g. polygonal cross sections are possible.
Preferably the dimensions of the coil are in the range of 8-12 mm and its length is in the range of 10-20 mm. Such dimensions advantageously permit the coil to form part of a capsule whose exterior is smooth and appropriately shaped and sized for ready ingestion. The use of an antenna as claimed is believed to obviate at least some of the space-inefficiency disadvantages of the Lambert et al capsule.
According to a second aspect of the invention there is provided an ingestible device delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator from the energy source; and a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range, the device including a ferrite core having coiled theraround a wire for coupling received electromagnetic radiation to the releasable latch, characterised in that the device comprises an elongate, hollow housing, the ferrite core being elongate with its longitudinal axis aligned with the longitudinal axis of the hollow housing.
The ferrite core and coil combination of the ingestible device delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator from the energy source; and a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range, the device including a ferrite core having coiled theraround a wire for coupling received electromagnetic radiation to the releasable latch, characterised in that the device comprises an elongate, hollow housing, the ferrite core being elongate with its longitudinal axis aligned with the longitudinal axis of the hollow housing also allows, in an alternative embodiment of the invention, highly efficient coupling of energy from a magnetic field to the circuitry forming part of the capsule. Thus this aspect of the invention allows the construction of an advantageously compact device whose energy efficiency is higher than that of prior art designs.
In preferred embodiments of the invention the receiver includes the ferrite core and coil combination as one of its circuit components. Either embodiment of the apparatus may optionally include a transmitter including a said air or ferrite core and coil combination. The air of ferrite core and coil preferably are spaced from any fluid within or outside the device by 0.1 to 1 mm. The air of ferrite core may have coiled therearound a wire for transmitting electromagnetic radiation.
The preferred operating regime for the device of the invention is between 1 MHz and 14 MHz. In addition to the biological effects there are a number of electromagnetic issues which influence the choice of operating frequency. One issue is restrictions on the use of the electromagnetic spectrum to prevent interference between various users. Thus 13.56 MHz is a preferred operating frequency as this frequency is designated for general industrial use. However, at this, the upper end, of the frequency range several adverse effects occur These include loading of the transmitter by the body tissue, skin effect adversely affecting the receiver impedance and induction heating of metal objects.
The selected frequency for use of the preferred embodiment of the invention is therefore at the lower end of the range, nominally between 1 MHz and 3.0 MHz.
The frequency effects therefore determine that the power transmitted to the device of the invention to energize the latch comes from a magnetic field of between 1.0 MHz and 3.0 MHz induced over the region of the body containing the capsule. The SSDC of the invention is designed with a means for extracting power from this magnetic field to energize the latch. It should be noted that the magnetic field has no corresponding electric field such as in a radiowave and as such there is energy stored in the field with minimal loss until a receiver is placed within the field capable of extracting the energy.
The preferred embodiment of the receiver is a coil of wire arranged so that the coil intercepts the field lines so that a voltage is induced across the coil by the time varying magnetic field. A capacitor connected across the coil tunes the circuit so that it has a resonant frequency equal to the frequency of the energizing field. When such a tuned receiver is placed in an oscillating magnetic field a high current is induced in the coil and this current generates a magnetic field of its own. It is the interaction of these fields that enables the receiver to extract significant amounts of real power from the energizing magnetic field. The power is accessed by connecting the latch electrical circuit in series or parallel with the coil/capacitor tuned receiver.
The magnitude of the power that can be extracted from the magnetic field is a strong function of the size and shape of the antenna (receiver coil). The voltage induced in the coil is proportional to its area and the power induced is proportional to the square of the voltage. Hence the power that can be extracted from the field is proportional to the fourth power of the diameter of the coil. In practice, the actual power is also modified by the permeability surrounding the coil and a shape factor relating to the length and the angular orientation of the coil to the field.
In a preferred embodiment of the invention an air cored design of receiver antenna has been developed which uses between 60 and 100 turns of copper wire in the range 0.1 mm to 0.3 mm diameter wound as a single or double layer cylindrical coil of diameter between 8 mm and 12 mm and length between 10 mm and 20 mm.
Care must be taken in the design to minimise the effective impedance of the receiver coil in order to maximise the Q of the circuit. Unwanted impedance can be added to the circuit from a number of sources:
Eddy currents in metallic components
Skin depth effects in the conductor
Dielectric loss in the tuning capacitor.
In addition the proximity of a conductive fluid to the coil can change the resonant frequency as it acts as an additional capacitance in parallel to the coil. It is therefore preferable to maintain a minimum separation of the coil from any internal or external fluid. This distance should be in the range of 0.1 mm to 1.0 mm.
According to a third aspect of the invention there is provided an apparatus for transmitting electromagnetic radiation to power an ingestible device, the apparatus comprising a support supporting a pair of transmitter coils including one or more loops operatively connectable to a source of oscillating electrical current, the support supporting the respective coils of the pair on opposite sides of the abdomen of an animal.
More specifically, the preferred approach used in this invention is inductive coupling at a frequency which gives high energy density but at which the absorption by body tissue is small compared to the energy coupled into the capsule. In this approach an alternating current is passed through one or more loops of a conductor such that an alternating magnetic field is generated between the loops. A preferred arrangement is to use two loops, one on either side of the abdomen. With this arrangement the amplitude of the magnetic field at any point between the loops can be accurately controlled. Thus, for example, two loops separated by their radius form a Hehmholtz pair giving a nominally uniform field over the full volume between the loops. In the invention the spacing between the loops would be between one radius and four radii. The preferred embodiment has a spacing between the loops equal to the diameter of the loop as this maximises the central field value for a given value of the reactive power of the field generator supply.
It should be noted that a coil pair will generate a combination of magnetic and electrostatic fields around it. The major one of interest is the magnetic field which, in radio terms, only exists in the near field. The design of the field generator uses appropriate shielding to minimise the longer range radio waves and the electrostatic fields.
The energy that can be transmitted by an alternating magnetic field is a function of its field strength, frequency and the mutual inductance between the energizing and receiving coils. The apparatus of the invention optimises those three variables to meet the needs of safe and reliable operation with readily available electronic components.
The use of a pair of current loops to generate the field is chosen to maximise the magnetic field in the useful volume between the loops whilst minimising near field electric field and far field electromagnetic radiation. This minimises any potential effects on persons close to the field generator from the electric field gradient and also minimises stray electromagnetic radiation which could interfere with other electrical equipment.
The maximum power level is achieved when the axis of the coil in the capsule is aligned with the axis of the coil of the external field generator. This cannot be guaranteed when the capsule is inside the GI tract.
In the prior art, arrangements have been made inside the capsule to ensure that the magnetic flux is guided through the receiver coil whatever the orientation. One example of this is the use of 3 orthogonal coils wound around a ferrite core with a 3 axis cross form, as disclosed in U.S. Pat. No. 5,167,626.
Within the size constraints of SSDC""s such arrangements are sub-optimal in their efficiency in interacting with the external field as they suffer from poor shape factor. The preferred arrangement in this invention is the use of a single coil geometry which has high efficiency only when the external magnetic field is orientated along its preferred axis and to provide a means of changing the orientation of the energizing field until it aligns with the capsule. Theoretically this can be achieved in a number of ways:
Rotating the mammal with respect to the energizing field
Rotating the field generator with respect to the mammal
Providing a plurality of energizing coils at different angular orientations and energizing them sequentially or in combination to rotate the orientation of the magnetic field in space until it is aligned to the capsule axis.
The preferred embodiment of the invention uses 3 coil pairs mounted orthogonally to each other. The coils are sized to permit e.g. a person to be positioned within the space enclosed by the coils. An example of the typical size of the coils would be 600 mm diameter and 600 mm apart.
To facilitate entry of the person to the central region e.g. the pair of coils with the vertical axis may be arranged so that part of one of the coils is contained on a door where continuity of the coil is provided by electrical connections on the door when it is closed; or one of the coils may be on a vertical slideway so that the person could stand at the correct location and the coils slid into position by moving vertically.
Another possibility is for the coil pairs to be supported on a wearable garment.
The energization of the magnetic field generator requires powering the field coils with current at the level necessary to generate the field at the required frequency of between 1.0 MHz and 14.0 MHz.
A typical field strength would be in the range 20 Amxe2x88x921 to 200 Amxe2x88x921. To generate this field strength coils with multiple turns can be used where the number of turns is chosen to match the capabilities of the electronic components driving the current. A preferred embodiment of the invention uses 2 turns per coil although other implementations may use from 1 to 10 turns per coil.
In order to minimise resistive heating at these frequencies large diameter conductors or Litz wire are preferred in the construction of the field coils, to minimise the effect of skin depth limiting current penetration into the wire.
The powering of the energizing coils is traditionally accomplished using a circuit comprising a low power oscillator, an r.f. amplifier and a matching network efficiently to couple the coils to the amplifier. Typically the oscillator is crystal controlled for frequency stability. This approach suffers from the problem that changes to the load impedance can reduce the field strength if the tuning of the matching unit becomes sub optimal due to, for example, the electrical effects of a body close to the coils.
In the apparatus of the invention the current is generated by using the field coils as part of the frequency determining components of a power oscillator directly driving the coils. The major advantage of this approach is that the field level remains constant even if the effective load impedance changes. This is achieved at the expense of a small change in frequency.
At the lower end of the preferred frequency range 1.0 MHz to 3.0 MHz the frequency shift caused by the presence or absence of people or small metal objects within the energized field volume is small compared with the bandwidth of the tuned receiver in the capsule and hence there is minimal change in the receiver power. This is considered a major improvement on prior art as it provides more reliable actuation.
The power oscillator can be implemented using any of a range of established oscillator circuits. The preferred embodiment uses a Hartly oscillator and achieves efficient performance by the use of 6 mm diameter copper tube for the coils and low dielectric loss capacitors for the passive components and a low loss, high voltage power MOSFET for the active component.
According to a fourth aspect of the invention there is provided a method of operating an ingestible device for delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, causing a mammal to ingest an ingestible device comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator from the energy source; and a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range; the receiver being capable of extracting energy from an oscillating magnetic field and the method comprising at a chosen time, generating at least one axial, oscillating magnetic field and directing the field at the abdomen of the mammal whereby the receiver intercepts the said field and triggers the latch to cause opening of the reservoir; and simultaneously inhibiting the generation of long wave radio waves and short wave electrostatic radiation in the vicinity of the said abdomen. Preferred features of the method are the step of generating two or more axial, oscillating magnetic fields whose axes are mutually skewed; the step of generating two or more axial, oscillating magnetic fields whose axes are mutually skewed and including the step of generating three said fields, wherein the axes of the said fields are mutually orthogonal; and the field is generated using a coil pair operatively connected to a source of an oscillating current.
It is desirable for an SSDC to indicate its location and status when in the GI tract. In particular it is important for the SSDC to indicate the precise moment at which the discharge of the substance from the reservoir occurs, and for the SSDC to indicate its location in the GI tract at or close to such a time.
For this reason it is known to include in an SSDC a transmitter that transmits a signal, indicative of the status and, optionally, the location of the SSDC, beyond the body of the mammal. One way of achieving the latter effect is to provide a radiolabelled marker within the SSDC, that may be tracked within the GI tract by means of known Gamma scintigraphy techniques.
U.S. Pat. No. 5,279,607 discloses an SSDC the operation of which is initiated by a receiver and latch combination. The receiver is a tuned resonant circuit, including a first antenna, that generates a current in a heating resistor when it couples, via the antenna, with an oscillating electromagnetic field of the same frequency as the resonant circuit, transmitted from outside the body of the mammal.
The heating resistor is positioned to heat a fusible component that holds a resiliently deformable member in an energy storage (ie. high potential energy) condition. On fusing of the fusible component a diaphragm moves and is ruptured by a pin. This causes two reagents to mix in a reaction chamber and generate a gas, the increasing pressure of which drives a piston to expel the substance from the reservoir of the SSDC.
The SSDC of U.S. Pat. No. 5,279,607 includes a second resonant circuit capable of acting as a transmitter of a signal intended to indicate emptying of the reservoir. The second circuit is initially isolated from the receiver circuit by an electrical short. A blade attached to the piston ruptures the short as it starts to move, thereby coupling the second resonant circuit to the electromagnetic field. This induces a current in the second circuit that is transmitted, via a further antenna, for receipt and processing by a receiver external to the mammal.
The SSDC of U.S. Pat. No. 5,279,607 suffers from the disadvantage that, because of the limited space within the capsule, the breakable short cannot be placed anywhere other than close to the initial position of the pistonxe2x80x94otherwise the short may encroach into space intended for storage of the substance; or the blade may be unacceptably large compared with the other components in the capsule.
Consequently the blade in U.S. Pat. No. 5,279,607 of necessity ruptures the short at the beginning of the travel of the piston. This means that the second resonant circuit may generate a signal indicative of discharge of the substance from the reservoir even when the SSDC fails to achieve this, e.g. through sticking of the piston or failure of the gas generating reagents to react completely.
Also if, as may be desirable or sometimes unavoidable in an SSDC, it is required to locate the second resonant circuit at a location spaced from the piston or other actuator that causes discharge of the substance, in the SSDC of U.S. Pat. No. 5,279,607 this may only be achieved at the expense of including comparatively long electrical connecting wires between the first circuit, the second circuit and the breakable short. This may complicate the process of assembly of the SSDC.
According to a fifth aspect of the invention there is provided a device for delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator mechanism from the energy source; a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range; and a transmitter of electromagnetic radiation for transmitting a signal indicative of operation of the device, the said reservoir including an exit aperture, for the substance, closed by a closure member that is sealingly retained relative to the aperture, the exit aperture being openable on operation of the actuator mechanism; wherein (i) the latch is thermally actuated; (ii) the energy source is held in a potential energy state by the latch until the latch operates; and (iii) the device includes a heater for heating the latch whereby, on the receiver detecting the said radiation the receiver operates to power the heater and thereby release the latch, permitting expulsion of the substance from the reservoir; characterized in that: the device also includes a restraint operable to limit operation of the actuator mechanism; and in that, on release of the latch, the restraint operates a switch to activate the transmitter for transmission of a said signal.
The inclusion of a restraint advantageously permits limiting of the movement or extent of operation of the actuator mechanism.
The use of the restraint to operate the switch confers considerable design freedom on a designer of a device according to the invention. In particular, the switch may be located conveniently close to a transmitter circuit even if the latter is remote from the actuation mechanism.
Preferred features of the fifth aspect of the invention are the actuator mechanism includes a moveable member moveable under power of kinetic energy from the energy source to promote expulsion of the substance from the reservoir; the restraint includes a flexible member interconnecting the moveable member and an anchorage fixed relative to the remainder of the device; and the switch includes a breakable, electrically conductive member, the flexible member and the breakable member being mutually engageable whereby on movement of the moveable member sufficiently partly or completely to expel or initiate expulsion of the substance from the reservoir the flexible member engages and breaks the breakable member to operate the switch; the actuator mechanism includes a piston moveable under power from the energy source for compressing the substance in the reservoir to promote its expulsion therefrom; the transmitter includes a resonant circuit connectable to draw power from the receiver; and the breakable member is an electrical short that electrically isolates the resonant circuit from the receiver until the flexible member breaks the breakable member; the length of the flexible member is such as to limit the travel of the moveable member to a chosen maximum; and the restraint and the switch are so dimensioned and/or located that the restraint operates the switch at a time corresponding to a predetermined amount of movement of the moveable member.
There are various possible approaches to providing an on-board energy source for the device.
In general terms to accomplish sufficient force and movement to expel the drug within a few seconds requires forces in the range 2 to 20N over distances of 2 mm to 20 mm. This typically amounts to a mechanical power level in the order of 0.1W or an energy of 0.1J. If the energy were stored in electrical form and used to drive an electromechanical actuator of simple form then typically the conversion efficiency would be less than 10%. An electrical energy storage system would then require to store 1J of energy and deliver it at 1W power. Micro-batteries as used in watches are of the necessary size and store easily sufficient energy; however they can only deliver that power at milliwatt rates. Capacitors however can deliver their energy at the required power levels but within the size constraint can only store millijoules of energy.
Several other forms of energy storage are theoretically possible including:
Chemical gas generation
Compressed nitrogen or air
Liquified propellant fluids (e.g. N2O, butane/propane, HFA""s)
Springs
Chemical heat generation
Chemical storage has potentially the highest energy density, but introduces issues associated with chemical compatibility, stability, triggering and toxicological safety.
Within the available space constraints there is sufficient volume to store the required energy either in springs or as a compressed gas, e.g. air both of which forms are possible as the energy can be released directly in the desired form of a force acting to cause mechanical motion. However the complexity of a device including a compressed air source may militate against its use.
According to a sixth aspect of the invention there is provided a device for delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator from the energy source; and a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range; the energy source including a compressed spring capable of acting on the actuator mechanism the expansion of which is initiatable by the latch and the work of the expansion of which causes operation of the actuator mechanism, characterized in that the spring, in its uncompressed state, has a minimum helical angle of 15xc2x0. Preferred features of the sixth aspect of the device are the spring includes a wire whose diameter is approximately 0.8 mm and the spring defines a hollow cylinder.
Another device according to a seventh aspect of the invention is an ingestible device for delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator from the energy source; and a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range; the energy source including a compressed spring capable of acting on the actuator mechanism the expansion of which is initiatable by the latch and the work of the expansion of which causes operation of the actuator mechanism, characterized in that the spring includes a pair of wires each coiled in loops to define a pair of hollow cylinder-like shapes, a first said cylinder-like shape being of a greater internal diameter than the outer diameter of the second said cylinder-like shape and the first cylinder-like shape encircling the second cylinder. An eighth aspect of the invention is an ingestible device for delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator from the energy source; and a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range; the energy source including a compressed spring the expansion of which is initiatable by the latch and the work of the expansion of which causes operation of the actuator mechanism, characterized in that the spring comprises a stack of resiliently deformable discs, the periphery of each disc having formed therein a series of waves, the waves of respective said discs connecting such that the peak of each wave contacts the trough of a wave of an adjacent said disc.
A device according to a ninth aspect of the invention is an ingestible device for delivering a substance to a chosen or identifiable location in the alimentary canal of a human or animal, comprising an openable reservoir, for the substance, that is sealable against leakage of the substance; an actuator mechanism for opening the reservoir; an energy source, operatively connected for powering the actuator mechanism; a releasable latch for controllably switching the application of power to the actuator from the energy source; a receiver of electromagnetic radiation, for operating the latch when the receiver detects radiation within a predetermined characteristic range; and a transmitter of electromagnetic radiation for transmitting a signal indicative of operation of the device; the said reservoir including an exit aperture, for the substance, closed by a closure member that is sealingly retained relative to the aperture, the exit aperture being openable on operation of the actuator mechanism; wherein (i) the latch is thermally actuated; (ii) the energy source is held in a potential energy state by the latch until the latch operates; and (iii)the device includes a heater for heating the latch whereby, on the receiver-detecting the said radiation the receiver operates to power the heater and thereby release the latch, permitting expulsion of the substance from the reservoir; characterized in that the device also includes (a) a restraint operable to limit operation of the actuator mechanism; (b) a switch for switchably operating the transmitter; and (c) a switch member operatively interconnecting the actuator mechanism and the switch such that operation of the actuator mechanism causes the switch member to operate the said switch.
Preferred features of the sixth, seventh and eighth aspects of the invention are defined in the claims depending from claims 39, 42, 50 and 69.
One preferred embodiment of the device includes a coil spring which operates to move a piston to expel the drug from inside the capsule through an opening at the other end of the capsule. An example of the dimensions and components that could be used would be for a volume of 1 ml available to contain the drug in the form of a cylinder 9 mm in diameter and 16 mm long. A coil spring of 8 mm outer diameter compressed to a length of 4.6 mm could exert an initial force of over 1 kg and have a residual force of 0.2 kg after it has travelled the 16 mm.